After the terror attack at the Boston Marathon yesterday, airlines and hotels offered to waive cancellation fees so that people could feel free to cancel their trips to Boston with no penalty. Nerves are jittery—which explains why a plane at Boston’s Logan Airport and a portion of LaGuardia Airport were evacuated today—but I’d be surprised if many people are cancelling trips to Boston. By now, nearly 12 years after 9/11, haven’t we all become a lot more acclimated to the fact that anything can happen anywhere at any time? The risk of a terror attack is just part of the new normal. You could be in a skyscraper in New York, at a nightclub in Bali, in a train station in Madrid, in a theater in Moscow, at a resort in Africa, on the subway in London, or on a street corner in Boston, and become the victim of a terror attack.

If the twin bombings had been in Istanbul, quite a few people might be cancelling their trips to Turkey right now—although probably much fewer than would have been the case a decade ago. Just how risky is it to go to Boston—or to Istanbul—right now? We don’t know—and therein, I think, lies our discomfort. When we make decisions about where to travel, we try to gauge the risk of going to a place by looking at the historical record. But, in a world of terror attacks, a place can be safe historically yet become unsafe in an instant. We don’t know how relevant the historical record is. Thus our jittery nerves.

Two factors determine what risks people are willing to take. One is risk perception—our estimation of how dangerous a place is. Two people can look at Boston, or Istanbul, and one person sees danger and the other doesn’t. The second factor is risk tolerance—each person’s individual threshold for danger—which determines our decisions about where we’re willing to travel to. First you estimate the risk, then you decide whether or not it’s tolerable. In the case of terror attacks, however, it’s impossible to estimate the risk. And, since anything can happen anywhere at any time, there is little you can do to reduce the odds of being involved in a terror attack or otherwise give yourself a sense of control over the situation. So how do we decide whether or not to cancel a trip?

One thing you can do is put the risk in perspective. A lot of people confuse the probability of a terror attack happening in a destination they’re headed to with the probability of being a victim of that terror attack. It is likely that there will be another terror attack somewhere in the United States within the next year. But does that translate into a high degree of risk for any individual citizen? No. If you were headed to Boston—or anywhere—tomorrow, you’d be more likely to die from a car accident, a heart attack, a gunshot wound, or just crossing the street, than from a terror attack. The best way to protect yourself? It’s not to cancel a flight to Boston. It’s to drive carefully on the way to the airport. And, once you're there, to look both ways before crossing Mass. Ave.